Grease is a semi-solid lubricant used to optimize the lubrication of mechanical systems, such as bearings, gears, and the like, which are key components for vehicular and industrial applications. Typically, grease is composed of base oil, a thickener, and additives.
The base oil is a component that is added to minimize a change in the viscosity of grease depending on the temperature. The base oil includes expensive ester oil, silicone oil, or fluorine oil, so the use thereof is limited due to problems such as high price. Hence, poly-alpha-olefin (PAO) synthetic base oil, which exhibits superior effects for the price, is mainly used. The thickener is a component that determines the main properties such as heat resistance and water resistance of grease. Since the properties of the grease may vary greatly depending on the choice of additive, the selection not only of the thickener but also of the appropriate additive is regarded as important. Furthermore, in order to improve the high-temperature durability life, an additive, such as an antioxidant, an extreme pressure additive, a corrosion inhibitor, etc., is used.
As technology for environment-friendly vehicles is being rapidly developed, research into the emotional design of the vehicle, which has not been considered in the past, is being actively carried out. Among them, the operating force and noise, vibration, and harshness (NVH) properties of parts that consumers may feel are the top priority. The best way to optimally exhibit the two properties is to change the design or materials and the grease properties. The case of design and material changes is problematic because of many factors to consider, such as costs, effects on surrounding parts, and the like, and thus realizing performance improvements through changes in the mixing design of grease is deemed to be effective.
Typically, operating properties and noise properties are in a trade-off relationship with each other, as shown in FIG. 1, due to the viscosity of the base oil constituting the grease, and when considering noise properties, there are many cases in which low-temperature operation becomes impossible. On the other hand, when considering low-temperature properties, development progresses in a manner in which operating noise is poor.
With the goal of exhibiting optimal performance, the existing grease mixing was performed at point {circle around (1)} shown in FIG. 1.
There is thus a need for grease capable of improving both noise properties and operating properties.